Power tools and other power apparatuses can generate substantial vibration during operation. Power tools may include, for example, reciprocating and/or rotating parts, such as, for example, motors, fan blades, bits, discs, and belts, which can cause the tool to vibrate during operation. An operator holding the tool can experience fatigue, pain, or injury because of the tool's vibration.
One example of a power tool that exhibits vibration during operation is a random orbital sander, which can be used in a variety of applications where it is desirable to obtain a smooth surface free of scratches and swirl marks. Such applications typically involve wood working applications such as furniture construction or vehicle body repair applications, just to name a few.
Random orbital sanders typically include a platen that is driven rotationally by a motor-driven spindle. The platen is driven by a freely rotatable bearing that is eccentrically mounted on the end of the drive spindle. Rotation of the drive spindle causes the platen to orbit about the drive spindle while frictional forces within the bearing, as well as varying frictional loads on the sanding disc attached to the platen, cause the platen to also rotate about the eccentric bearing, thereby imparting the “random” orbital movement to the platen. Such random orbit sanders often also include a fan member that is driven by the output shaft of the motor. The fan member is adapted to draw dust and debris generated by the sanding action up through openings formed in the platen and into a filter or other like dust collecting receptacle.
One such prior art random orbital sander is disclosed in U.S. patent application Ser. No. 11/103,928, the entire disclosure of which is incorporated herein by reference for all purposes. For context, a short section of the '928 application describing a random orbital sander is repeated here. With reference to FIG. 9, a random orbital sander 10 generally includes a housing 12 that includes a two-piece upper housing section 13 and a two-piece shroud 14 at a lower end thereof. Removably secured to the shroud 14 is a dust canister 16 for collecting dust and other particulate matter generated by the sander during use. A platen 18 having a piece of sandpaper 19 (shown in FIG. 10) releasably adhered thereto is disposed beneath the shroud 14. The platen 18 is adapted to be driven rotationally and in a random orbital pattern by a motor disposed within the upper housing 13. The motor (shown in FIG. 10) is turned on and off by a suitable on/off switch 20 that can be controlled easily with a finger of one hand while grasping the upper end portion 22 of the sander. The upper end portion 22 further includes an opening 26 formed circumferentially opposite that of the switch 20 through which a power cord can extend.
The shroud 14 can be is rotatably coupled to the upper housing section 13 so that the shroud 14, and hence the position of the dust canister 16, can be adjusted for the convenience of the operator. The shroud section 14 further includes a plurality of openings 28 (only one of which is visible in FIG. 9) through which a cooling fan driven by the motor within the sander can expel air drawn into and along the interior area of the housing 12 to help cool the motor.
With reference now to FIG. 10, the motor can be seen and is designated generally by reference numeral 30. The motor 30 includes an armature 32 having an output shaft 34 associated therewith. The output shaft or drive spindle 34 is coupled to a combined motor cooling and dust collection fan 36. In particular, the fan 36 includes a disc-shaped member having impeller blades formed on both its top and bottom surfaces. The impeller blades 36a formed on the top surface of the fan serve as the cooling fan for the motor, and the impeller blades 36b formed on the bottom surface of the fan serve as the dust collection fan for the dust collection system. Openings 18a formed in the platen 18 allow the fan 36b to draw sanding dust up through aligned openings 19a in the sandpaper 19 into the dust canister 16 to thus help keep the work surface clear of sanding dust. The platen 18 is secured to a bearing retainer 40 via a plurality of threaded screws 38 (only one of which is visible in FIG. 10) that extend through openings 18b in the platen 18. The bearing retainer 40 carries a bearing 42 that is journalled to an eccentric arbor 36c formed on the bottom of the fan member 36. The bearing assembly is secured to the arbor 36c via a threaded screw 44 and a washer 46. It will be noted that the bearing 42 is disposed eccentrically to the output shaft 34 of the motor, which thereby imparts an orbital motion to the platen 18 as the platen 18 is driven rotationally by the motor 30.
With further reference to FIG. 10, a braking member 48 is disposed between a lower surface 50 of the shroud 14 and an upper surface 52 of the platen 18. The braking member 48 can include an annular ring-like sealing member that effectively seals the small axial distance between the lower surface 50 of the shroud 14 and the upper surface 52 of the platen 18.
With reference to FIG. 11, the braking member 48 includes a base portion 54 having a generally planar upper surface 56, a groove 58 formed about the outer circumference of the base portion 54, a flexible, outwardly flaring wall portion 60 having a cross sectional thickness of preferably about 0.15 mm, and an enlarged outermost edge portion 62. The groove 58 engages an edge portion 64 of an inwardly extending lip portion 66 of the shroud 14, which secures the braking member 48 to the lip portion 66. In FIGS. 10 and 11, the outermost edge portion 62 is illustrated as riding on an optional metallic (e.g., stainless steel) annular ring 61 that is secured to the backside 52 of the platen 18. Alternatively, the entire backside of the platen 18 may be covered with a metallic or stainless steel sheet. While optional, the stainless steel annular ring or sheet 61 can serve to substantially eliminate the wear that might be experienced on the upper surface 52 of the platen 18 if the outermost edge portion 62 were to ride directly thereon.